A mobile telephone station in standby mode must monitor the appropriate control channel of the system in which it is located in a manner such that the mobile telephone station receives all system control messages addressed to it. This necessarily requires that the mobile telephone station monitors the control channel during any time periods within which control messages directed to that mobile telephone station could possibly be transmitted.
In systems such as the EIA/TIA-553 system (AMPS), the Total Acccess Communications System (TACS), and the D-AMPS IS-136 system, a mobile telephone station in standby mode, receives successive word blocks on a forward control channel (FOCC). Each word block consists of a 10-bit dotting sequence, an 11-bit word synchronization sequence, and ten word repeats each containing 40 bits. The word repeats are separated into two time-multiplexed data streams, the A stream and the B stream, each consisting of five word repeats. Depending on the last digit of the subscriber number, a mobile telephone station in standby mode listens to either the A stream or the B stream.
In the above systems, when the mobile telephone station monitors the forward control channel, the receiver is constantly on in that all five repeats of a word within a word block, are received, whereupon a majority decision is made, and BCH (Bose-Chaudhuri-Hocquenqhem) decode operations and parity check operations are performed. Thus, battery power is consumed in a mobile telephone station also in the standby mode. Moreover, this power consumption of the receiver of the mobile telephone station, when the mobile telephone station is monitoring the forward control channel, is a significant percentage of the total power consumption of the mobile telephone station.